1. Field of the Invention
The present invention relates to an optical fabrication method which performs a step of forming a powder layer of a predetermined thickness and then sintering the powder layer with a light beam, a predetermined number of times, and cuts the periphery of the powder layers.
2. Description of the Related Art
In the technical field of forming three-dimensional fabricated articles by sintering metal or non-metal powder with a light beam like a laser beam, various methods have already been proposed. Each of the methods includes:
(1) a dispersion and planarization step of dispersing powder falling down and smoothing an upper surface of the dispersed powder or near the upper surface;
(2) a step of irradiating a fabrication area with a light beam like a laser beam to sinter the irradiated area; and
(3) a step of forming the periphery of a single layer or a plurality of layers subjected to the sintering step (2) while cutting the peripheral edge portion(s) thereof with an end mill, and the above steps (1), (2) and (3) are repeated to form finally necessary three-dimensional shapes.
According to the conventional techniques, as disclosed in Japanese Unexamined Patent Application Publication (Translation of PCT Application) Nos. Hei 8-502703 and 2003-502500, in the sintering step (2), the degree of irradiation in the fabrication area of an irradiation surface as shown in FIG. 1 is kept approximately constant and is not particularly adjusted in the area.
It is needless to say that while the hardness and density of an object to be fabricated naturally change according to the degree of sintering, the object to be fabricated should not necessarily be demanded of constant hardness and density over the entire area.
There are a lot of cases where while higher hardness and higher density are required at the peripheral portion of the surface of the object to be fabricated, high hardness and high density are not always required in the center portion of the surface of the object to be fabricated.
However, there may be the opposite but rare case where low hardness and low density are required at the peripheral portion of the surface of the object to be fabricated and high hardness and high density are required in the center portion of the surface of the object to be fabricated.
In this case, irradiating a light beam of about the same intensity over the entire fabrication area as done according to the conventional techniques means to perform irradiation with a wasteful light beam, and is inadequate in terms of the fabrication speed and fabrication cost.
What is more, when objects to be fabricated sintered in such a way as to provide approximately the uniform hardness and density are coupled together as individual constituting portions as done in the conventional techniques while the hardness and density are needed to be sequentially changed, rapid changes in hardness and density occur at the coupled boundary portions. This results in a lot of defects, such as separation and cracking.
Such a case brings about basic shortcomings, such as leakage of a liquid like passing water, and reduction in the required mechanical strength, in the pipe structure which needs to pass a fluid.
While Japanese Patent No. 3446733 discloses high-density sintering of the surface of a powder sintering portion, the invention disclosed therein fails to assume on sequential adjustment of the hardness and density over the entire sintering area.